On Codeplex, a great project MOSS Faceted Search is available. It is just a great set of webparts which enhances the search experience in value a lot for your end users. It allows for drill down functionality in the search results based on so called facet values. A facet is a category your items, documents, ... can belong to. When you install the default project, your items, documents, ... are immediately grouped in different categories / facets: By Author By Content Type By Content Source Off course, you can add your own facets.